The present invention relates to a process for preparation of flock fibers suitable for use in the manufacture of pile materials by electrostatic flocking. The inventive process comprises treating man-made flock fibers with an aqueous solution containing tannin, a water-soluble alum, and preferably also a water-soluble-alkali- or ammonium salt.
The manufacture of plush, velvet, suede, and the like by the application of short fibers, called flock, to an adhesive-coated base under the influence of a high tension electrostatic field is a well-known process, described for example in U.S. Pat. Nos. 2,173,032 and 2,173,078. To obtain a dense and uniform pile, it is necessary to use flock fibers of distinct qualities. The fibers must have good flow and gliding properties allowing an easy supply from a hopper and a smooth passage through any sieves in the flocking apparatus, and they must possess a good spring capacity in an electric field, i.e. the fibers must be able to spring quickly from the supplying electrode to the adhesive-coated base acting as a receiving electrode. For good gliding properties and especially for a good spring capacity in a high tension electrostatic field the electric conductivity of the flock fibers is of greatest importance.
It is known that synthetic fibers made from polymers, such as polyamides, polyesters or polyacrylonitriles have a poor electric conductivity. If unprepared flock fibers of these polymers are used for electrostatic flocking, the fibers tend to cling to each other and to the electrodes, and they spring only slowly or not at all; frequently they also form thick, hard clusters of fibers which cannot pass through the sieves. It is therefore known that synthetic fibers require a preparation with chemical agents in order to obtain the necessary electric conductivity and a good spring capacity in a high tension electrostatic field.
Various chemical agents have been suggested for this purpose. U.S. Pat. No. 3,203,821 describes the use of a combination consisting of an anti-electrostatic agent, a ferro-electric substance, and an agent to improve gliding properties. As examples of antistatica, sodium salts of condensation products of fatty acids and sarcosin, phosphoric acid esters, or anion-active derivatives of polyvinyl alcohol are mentioned, and as ferro-electricum, potassium sodium tartrate, and as agents to improve gliding properties, boric acid or sodium sulphate are recommended.
German Pat. No. 1,098,913 proposes treatment of the fibers with anti-electrostatic agents, such as polyglycol esters or phosphoric acid esters with addition of potassium and sodium salts. U.S. Pat. No. 3,345,980 discloses the use of amphoteric compounds containing both a sodium sulphonate group and a tertiary amine group, and U.S. Pat. No. 3,498,816 recommends the use of quaternary ammonium compounds and of urea with the addition of wetting agents and acrylic polymers.
U.S. Pat. No. 3,322,554 describes a process for treatment of the fibers with tannin and potassium antimonyl tartrate, eventually followed by a treatment with anionic finishing agents and alkali- or ammonium salts or preceded by a treatment with an alum. Flock fibers prepared according to this process possess the required conductivity and show a good spring capacity in an electrostatic field.